The present invention relates to polymers which are inherently tacky and, as formed, are functional as pressure-sensitive adhesives. More particularly, the adhesives of the instant invention have excellent room- and low-temperature performance and provide an ecologically safe replacement for solvent adhesives and many acrylic- and rubber-based emulsion adhesives. The adhesives of the instant invention are prepared by emulsion polymerization.
Adhesives are provided as solvent polymers, bulk polymers and emulsion polymers. Some exist as pressure-sensitive adhesives, while others require tackification to achieve this end.
In respect of the instant invention, U.S. Pat. No. 3,275,589 to Alexander, et al. pertains to an adhesive for adhering polyolefin and similar hydrophobic polymers to themselves and to other materials. The polymers disclosed are tacky, but not pressure-sensitive adhesives and are obtained by the polymerization of 100 parts by weight of a monomer mixture comprising 30 to 40 parts by weight vinyl acetate and, correspondingly, 60 to 70 parts by weight of (a) a monoalkyl ester of an alpha beta ethylenically unsaturated monocarboxylic acid such as 2-ethyl hexyl acrylate, or (b) a dialkyl ester of an alpha beta ethylenically unsaturated dicarboxylic acid such as 2-ethyl hexyl maleate, or (c) a mixture of the two. When three monomers are employed, the three illustrated include vinyl acetate, di-2-ethyl hexyl maleate and 2-ethyl hexyl acrylate.
U.S. Pat. Nos. 4,507,429, 4,694,056, and 4,725,639 to Lenney, and assigned to Air Products, Inc., pertain to a pressure-sensitive adhesive composition, and the products and method of making them, comprising a polymer of an acrylic ester and/or vinyl ester, an olefinically unsaturated carboxylic comonomer, and a polyolefinically unsaturated copolymerizable monomer employed to enhance the adhesive strength of the polymer. The polymer is formed by an aqueous emulsion polymerization in the presence of a stabilizer system containing hydroxy propyl methylcellulose and an ethoxylated acetylenic glycol. Product glass transition temperature may be as high as -15.degree. C., limiting utility at reduced temperature.
U.S. Pat. Nos. 4,753,846, 4,826,938 and 4,829,139, all to Mudge and assigned to National Starch & Chemical Corporation, pertain to an ethylene containing pressure-sensitive adhesive produced by high-pressure emulsion polymerization in which the adhesive comprises a polymer of 30 to 70 percent by weight of a vinyl ester of an alkyl acid such as vinyl acetate, 10 to 30 percent by weight of ethylene, 20 to 40 percent by weight of di-2-ethyl hexyl maleate, and 1 to 10 percent by weight of a monocarboxylic acid such as acrylic acid. Again, glass transition temperature may be as high as -25.degree. C., also limiting low-temperature utility.
U.S. Pat. No. 4,322,576 assigned to Wacker Chemie GmbH also pertains to ethylene containing vinyl acrylate polymers also produced and formed by high-pressure emulsion polymerization. Dialkyl esters of dicarboxylic acids are not employed as monomers.
We have sought to develop pressure-sensitive adhesives of controlled properties which serve to supplant a multitude of solution and emulsion polymers by having broad utility and excellent adhesive properties at ambient and low temperatures. This is the subject of the instant invention.